To prevent damage to the read-write head and to the magnetic storage disk when a disk drive is not in use, the disk drive “soft parks” or “hard parks” the head in a safe position with respect to the disk. Soft parking refers to parking the head when the disk drive will remain powered on after the park. For example, the disk drive typically soft parks the head during an extended period of non use such as a sleep or power-conservation mode. Conversely, hard parking refers to parking the head when the disk drive will be powered off after the park such as when one powers down a personal computer.
According to one technique for hard parking a read-write head, the disk drive moves and retains the head over the center or other portion of the disk where there is no stored data. Typically, a magnetic latch retains the head in the hard-park position until the disk is powered on. Thus, if the parked head contacts the disk, no data will be lost and the data-storage areas of the disk will be undamaged. Such contact may occur if one jostles the disk drive or the computer system incorporating the disk drive.
Unfortunately, this hard-parking technique is often unsuitable for laptop computers because they are often subjected to movements that are sufficient to jar the head loose from its parked position. As discussed below, an unrestrained head may be damaged, may corrupt stored data, or may damage the disk. Specifically, laptop computers, unlike desktop computers, are carried in many orientations and are jostled relatively frequently and forcefully. At times, this jostling may be sufficient to disengage the parked head from the magnetic retaining latch, particularly when the laptop is positioned such that gravity tends to pull the head out of the latch. Once disengaged from the latch, further jostling may cause the head to contact the data-storage areas of the disk. Such contact with the disk may corrupt stored data, permanently render the contacted area of the disk unable to store data, or damage the head or the arm to which the head is attached. But even if the jostling of the unparked head causes no data loss or damage, contact between the head and the data-storage areas of the disk as the disk starts to rotate upon power up may cause the data corruption or damage described above.
Referring to FIGS. 1A and 1B, a prior-art hard-parking/-unparking technique suitable for laptop computers is discussed.
FIG. 1A is a top plan view of a disk drive 10, which includes a disk 12 and parking platform 14 upon which the disk drive 10 hard parks an upper read-write head 16. Typically, the platform 14 is plastic and is positioned such that when one is carrying a laptop (not shown) in a normal carrying orientation, the platform 14 is between the ground and the disk 12 such that gravity tends to reinforce the parking of the head 16 on the platform 14. Therefore, the head 16 is less likely to fall off the platform 14 and contact the disk 12 if the laptop is jarred.
Still referring to FIG. 1A, the disk drive 10 also includes a read-write head assembly 18, which includes the head 16 and a motor assembly 20—sometimes called a voice coil motor—for moving the head 16 over the disk 12 during read and write cycles and for parking and unparking the head 16. The motor assembly 20 includes a stationary housing 22 containing one or more permanent magnets (not shown), a head-support arm 24 pivotally mounted to a post 26 and having a first end to which the head 16 is mounted and having a second end that extends into the housing 22, and an electronic coil (not shown in FIG. 1A) mounted to the second end of the arm 24. Alternatively, the coil is mounted to or within the housing 22 and the one or more permanent magnets are mounted to the second end of the arm 24.
FIG. 1B is a cut-away side view of the disk 12 and the platform 14 taken along lines AA of FIG. 1A. The platform 14 has an approximately level parking surface 28 and a ramped side wall 29, which extends from approximately the same level as the upper surface of the disk 12 to the parking surface 28. Typically, the ramped side wall 29 makes an angle of approximately 30°–60° with respect to the upper surface of the disk 12. For disk drives having a lower read-write head (not shown) in addition to the upper head 16, the platform 14 can be modified accordingly.
Referring to FIGS. 1A and 1B, the park and unpark procedures of the disk drive 10 are discussed. To hard park the read-write head 16, motor-assembly control circuitry (not shown in FIGS. 1A and 1B) drives a current through the coil (not shown in FIGS. 1A and 1B). The magnetic field generated by the energized coil interacts with the magnetic field generated by the one or more permanent magnets in the housing 22 such that the arm 24 pivots about the post 26 and moves the head 16 from a position over the disk 12 (dashed outline), up the ramped side wall 29, and onto the parking surface 28. Once the head 16 is parked on the surface 28, the laptop computer powers down the disk drive 10. To unpark the head 16, the laptop computer first powers up the disk drive 10. Once the disk 12 is rotating at its steady-state speed, the control circuitry energizes the coil such that the arm 24 pivots about the post 26 and moves the head 16 off of the parking surface 28, down the ramped side wall 29, and to a position over the disk 12. Although this technique may be suitable for soft parks and unparks in some applications, the disk drive 10 typically employs another technique for soft parking and unparking the head 16.
To prevent damage to and failure of the disk drive 10 during hard parking/unparking, the disk-drive manufacturer typically specifies the respective speed ranges—typically around 5 inches per second (IPS)—at which the read-write head 16 should be traveling during the above-described hard parking and unparking procedures. If the head 16 is traveling too fast during parking, then it may slam into the ramped side wall 29 at an excessive speed. This may damage the head 16, the motor assembly 20, or the platform 14. In addition, the speeding head 16 may scrape particles from the side wall 29, and these particles may contaminate and damage the disk 12. Likewise, if the head 16 is traveling too fast during unparking, it may bounce off of and thus damage the disk 12. Conversely, if the head 16 is traveling too slowly during parking, then it may have too little momentum to climb the ramped side wall 29 onto the parking surface 28. Likewise, if the head 16 is traveling too slowly during unparking, it may have too little momentum to leave the surface 28 and travel down the side wall 29.
Unfortunately, conventional motor-assembly control circuits (not shown in FIGS. 1A and 1B) are often unsuitable for implementing the hard-parking/-unparking technique described above in conjunction with FIGS. 1A and 1B. During normal read and write cycles, such a control circuit typically operates in a closed-loop configuration, relying on servo signals to indicate the position of the read-write head 16 relative to the disk 12. These servo signals are embedded in the data-storage areas of the disk 12, are read by the head 16, and are fed back to the control circuitry, which uses the fed-back servo signals to control the movement of the head 16. But during the last portion of the hard parking procedure and the initial portion of the hard unparking procedure, the head 16 is beyond the periphery of the disk 12 and thus cannot read the servo signals. Therefore, when the head 16 is beyond the disk periphery, the control circuit does not receive the servo signals and thus effectively operates in an open-loop configuration. Unfortunately, while operating in an open-loop configuration, the control circuit may cause the coil to move the head 16 at speeds that lie outside the respective ranges specified for the hard park and unpark speeds.